1. Field of the Invention
The present invention relates to bellow actuators which are expansible and contractible in response to pressure variations.
2. Description of Related Art
Prior art inflatable bellows devices include those disclosed in U.S. Pat. No. 4,464,980 issued Aug. 14, 1984 to Hideo Yoshida, for a bellows actuator blow-moulded from thermoplastic elastomeric material, U.S. Pat No. 3,469,502 issued Sep. 30, 1969 to Robert I. Garner for a flexible bellows with a nesting convolution contour and a relatively large deflection ratio, U.S. Pat. No. 3,731,595 issued May 8, 1973 to R. Wentworth Jr. for a cylindrical bellows seal for extensive axial movement U.S. Pat. No. 4,183,289 issued Jan. 15, 1980 to Takeshi Jinnouchi for a bellows apparatus with guide members restricting elongation and contraction, and U.S. Pat. No. 4,745,848 issued May 24, 1988 to Kurt Hennig for a bellows with a pleated cover and two pleated arms. All of the above-mentioned prior patents disclose variations on traditional bellow designs with circular or rectangular cross-sections.
In contrast, U.S. Pat. No. 4,939,982 issued Jul. 10, 1990 to Guy Immega and Mirko Kukolj is an axially contractible actuator designed to pull rather than push on a load.
The important characteristics of bellows actuators include pressure rating, percent elongation, elastic deformation of the membrane and axial rigidity.
Bellows with a rectangular cross-section are not generally suitable for actuators since they deform radically to a cylindrical shape under pressure.
Bellows with a circular cross-section can be made to withstand higher pressures but the percentage elongation is restricted by the need for elastomeric deformation of the bellows membrane.
Bellows with a circular cross-section which are made from metal generally can withstand greater pressure but have smaller elongation capability, unless equipped with special convolutions, as taught for example by the above-mentioned U.S. Pat. No. 3,469,502 Robert I. Garner, to allow for greater elastic deformation.